The present invention relates to a light beam detection device.
The use of a laser light source as a light source for an optical signal used in optical communications is widely known in the prior art. In general, the light output from such laser light source is an invisible light (for example, infrared light) having a wavelength longer than that of visible light. Thus, even if the optical signal or the light transmitted with an optical fiber cable is discharged from one end of an optical fiber cable, the location of the optical path formed by the optical signal is not visual.
An optical element (for example, a diffraction grating, a mirror, and the like) used in an optical communication module is tested by irradiating an infrared light from one end of the optical fiber cable onto the optical element, which is arranged on a sample stage. The optical element is then evaluated based on the light reflected from the optical element. Thus, in order to properly irradiate the infrared light on the optical element, the optical path location of the infrared light needs to be detected and focused onto the optical element. The intensity of the infrared light generally irradiated as the light is maximum in a central portion of a spot of light and the intensity gradually decreases as the spot central portion becomes farther away and the edge of the spot becomes closer. The intensity distribution is referred to as a Gaussian distribution and has a shape similar to that of a normal distribution. When irradiating the infrared light onto the optical element, an effective spot diameter of the central portion of the infrared light must be recognized to perform irradiation at the maximum intensity.
A detector for detecting the infrared light used in such a task includes an IR card, an infrared CCD camera, an optical power meter and the like.
The IR card has, on a surface of the card, a light-emitting region applied with a substance that emits visible light in accordance with the intensity of the received infrared light. Therefore, the optical path location of the infrared light is detected by visibly recognizing the light-emitting region.
The infrared CCD camera directly receives the infrared light and displays the intensity thereof on a display. This enables the shape of the intensity distribution of the infrared light to be observed. Further, the optical path location is easily detected due to the high sensitivity.
The optical power meter receives the infrared light with a sensor portion including a light-receiving element and displays the intensity of the infrared light on a meter. The optical path location is detected by moving the sensor portion to detect the position where the displayed intensity becomes maximum (refer to, for example, Japanese Laid-Open Patent Publication No. 6-236574).
In Japanese Laid-Open Patent Publication No. 6-236574, a light-receiving element divided into four portions is used as the sensor portion. A differential output for every two of the divided portions is input to an X-axis and a Y-axis of a two-channel oscilloscope. Then, the optical path location of the infrared light is identified and the sensor portion is positioned by looking at the emission point appearing on the cathode-ray tube of the oscilloscope.
The IR card has low sensitivity and does not have an amplification function. Thus, the entire working environment must be darkened to detect infrared light that has very weak intensity. Therefore, after darkening the room and detecting the optical path location of the light, an additional task of lighting the room and adjusting the arrangement position of the optical element becomes necessary. This is burdensome. Furthermore, since the sensitivity of the IR card is low and the boundary between the light-emitting portion and the non-light-emitting portion is unclear, the size of the effective spot diameter of the light having a Gaussian distribution cannot be determined. With regard to the infrared CCD camera, the body thereof is large and is not suited for detecting the infrared light in a tight space.
In the optical power meter of Japanese Laid-Open Patent Publication No. 6-236574, when searching for the optical path location, the sensor portions are arranged while looking at a cathode-ray tube. This causes frequent movement of sight and requires a long time to detect the optical path location.
In the above mentioned IR card, the infrared CCD camera, and the optical power meter, after the optical path location is detected, the optical element subjected to testing must be rearranged with respect to the detected optical path location. Thus, it is difficult to accurately irradiate the infrared light onto the optical element.